Hitherto, a fluorine-containing acrylate polymer is used as an active component of a water- and oil-repellent agent. Side chain fluoroalkyl groups in practically used fluorine-containing acrylate monomers usually have at least 8 carbon atoms. There is a defect that the fluorine-containing acrylate monomer is excessively hydrophobic since the length of the fluoroalkyl chain is long. The excessive hydrophobicity has caused various problems on the preparation and properties of the fluorine-containing acrylate polymer.
When an emulsion polymerization is used for the preparation of the fluorine-containing acrylate polymer, there are problems that emulsifiers should be used in a large amount and the types of the emulsifiers are limited, and that an auxiliary solvent should be used because of poor solubility with another fluorine-free monomer. When a solution polymerization is used for the preparation of the fluorine-containing acrylate polymer, there was the problem that the fluorine-containing acrylate monomer has low solubility in a polymerization solvent so that a sufficient monomer solution cannot be obtained.
As to the properties of the fluorine-containing acrylate polymer, there is the problem that sufficient water repellency cannot be imparted to the substrate. This problem seems to be caused by excessive hydrophobicity given by the long fluoroalkyl group.
Various up-to-date research results indicate that in view of the practical treatment of fibers with the surface treatment agent (particularly the water- and oil-repellent agent), the important surface property is not a static contact angle, but is a dynamic contact angle, particularly a reversing contact angle. That is, the advancing contact angle of water is not dependent on the carbon number of the fluoroalkyl side chain, but the reversing contact angle of water in the case of carbon number of at most 7 is remarkably low than that in the case of carbon number of at least 8. In correspondence to this, an X ray analysis shows that the side chain crystallizes when the carbon number of side chain is at least 7. It is known that the practical water repellency has the relationship with the crystallization of the side chain and that motility of the surface treatment agent molecules is an important factor for revelation of the practical performances (for example, MAEKAWA Takashige, FINE CHEMICAL, Vol. 23, No. 6, page 12 (1994)). Accordingly, it is believed that the acrylate polymer having low carbon number of fluoroalkyl group in the side chain which is at most 7 (particularly at most 6) has low crystallinity so that the polymer cannot satisfy the practical performances (particularly water repellency).
JP-A-63-90588, JP-A-63-99285 and JP-A-01-315471 disclose that a fluorine-containing acrylate polymer wherein the alpha-position is substituted with fluorine, chlorine or the like has good properties such as good adhesion to a substrate, high strength of a film and good water- and oil-repellency. These publications describe that the fluoroalkyl group used in Examples has at least 8 carbon atoms and does not suggest to use the acrylate monomer having the fluoroalkyl group having at most 6 carbon atoms.
Recent study results (EPA Report “PRELIMINARY RISK ASSESSMENT OF THE DEVELOPMENTAL TOXICITY ASSOCIATED WITH EXPOSURE TO PERFLUOROOCTANOIC ACID AND ITS SALTS” (http://www.epa.gov/opptintr/pfoa/pfoara.pdf)) and the like clarify that a PFOA (perfluorooctanoic acid) doubtfully has a potential risk of environmental load. EPA (Environmental Protection Agency of USA) announced on Apr. 14, 2003 that the EPA intensifies the scientific investigation on PFOA.
On the other hand, Federal Register (FR Vol. 68, No. 73/Apr. 16, 2003 [FRL-2303-8]) (http://www.epa.gov/opptintr/pfoa/pfoafr.pdf), EPA Environmental News for release Monday April, 2003 “EPA INTENSIFIES SCIENTIFIC INVESTIGATION OF A CHEMICAL PROCESSING AID” (http://www.epa.gov/opptintr/pfoa/pfoaprs.pdf), and EPA OPPT FACT SHEET Apr. 14, 2003 (http://www.epa.gov/opptintr/pfoa/pfoafacts.pdf) announced that a “telomer” may possibly metabolize or decompose to PFOA. It is also announced that the “telomer” is used in a large number of commercial products including fire fighting foams, care products and cleaning products as well as soil, stain and grease resistant coating on carpets, textiles, paper, and leather.